After an enraged drug addict points a gun at Chen and other staff members, the exasperated Carter leads a divisive walkout. He is frustrated that his request for metal detectors has been delayed, endangering lives. Meanwhile, Lewis counsels an exhausted elderly woman, Mrs. Berk (Shirley Knight - Divine Secrets of the Ya-Ya Sisterhood), whose adult son is dying from Huntington's Disease, the same affliction that killed Mrs. Berk's husband. Pratt cares for his developmentally disabled brother, Leon (Marcello Thedford), and comforts Chen after the gun incident. Kovac treats an HIV-infected child and becomes curious about the boy's parents. And Abby's brother, Eric (recurring guest star Tom Everett Scott - That Thing You Do!), witnesses more than he expected when he visits the hospital.